Carbonate and Bicarbonate

A variety of mineral addition calculators such as those by Promash, Beersmith, or Brewater report the concentration of carbonate added with the addition of minerals like chalk. This article will help you understand why we don’t use carbonate concentration in brewing chemistry and why we do use bicarbonate concentration.

Carbonate (CO3) and bicarbonate (HCO3) are virtually the same thing excepting for an important factor...their electrical charge. Carbonate has a -2 charge while bicarbonate has a -1 charge due to the extra hydrogen proton it contains. When we deal with brewing water chemistry, we are actually working with ‘equivalents’ which is equal to the weight of the molecule divided by its electrical charge. The molecular weight of carbonate is 60 grams and bicarbonate is 61 grams. Dividing by their electrical charge results in 30 grams per equivalent for carbonate and 61 grams per equivalent for bicarbonate. So you can see that there is almost a 2 to 1 difference in their equivalents. Big difference!

Another important factor in dealing with these ions is that the pH of the solution they are in has a profound effect on whether they exist as carbonate or bicarbonate ions. The figure below shows how the proportion of these ions varies with solution pH. Since wort and beer more commonly have pH under 6, you can see that there is NO carbonate content in that pH range. In fact, the pH would have to be above 8.3 to have 1 percent carbonate. Therefore in brewing chemistry, there is no chance for carbonate to exist in our water or wort. Any carbonate picks up an extra hydrogen proton and converts itself into bicarbonate. So, bicarbonate is the ion we should be quantifying when working with brewing chemistry.

This is the reason that Bru’n Water converts all alkalinity producing mineral additions into their corresponding bicarbonate concentrations for use in the program. For example, 1 gram of chalk in 1 gallon of water produces 158 ppm of carbonate. Bru’n Water reports that this same addition produces 322 ppm of bicarbonate and does not report carbonate concentration since it doesn’t exist at our brewing pH. Similar conversion is made when pickling lime (Ca(OH)2) is used in the program.

So it is important to convert these alkaline additions into their equivalent bicarbonate concentrations. Bru'n Water does this automatically. The other calculators mentioned above don't understand this chemistry fact.